Every concert in St Paul's is a conversation - between the performers and the cathedral's unique, reverberant acoustic. The combination of Mark Elder's performance, with the Hallé orchestra, of Bruckner's Seventh Symphony and Christopher Wren's architecture was a magnificent experience: a magical fusion of music, space and sound.

Right from the symphony's start, the huge acoustic of St Paul's worked a strange alchemy on Bruckner's music. The soaring cello melody that opens the piece sounded like a memory of ancient plainchant, a tune tinged with memories of arcane liturgy. Bruckner's music is often criticised for being episodic, but instead of sounding like a series of unconnected blocks of sound, the echoes that rang in the air after each climax in St Paul's meant that the whole symphony was connected by reverberant sonic haloes. In concert halls, Bruckner's music is full of pauses and silence, but in the Hallé's performance, there were no pauses, just spaces for the sound to echo into the vastness of the building.

Elder's brilliance was to use this acoustic as part of his interpretation. In the first movement, he built a coda of gigantic power, turning the Hallé players into a gigantic organ, whose final chord reverberated with an intense, major-key radiance.

But the huge slow movement was the heart of his performance. Elder cast the piece as a single arc of tension that culminated in a tumultuous climax, which seemed to expand the dimensions of the piece and push at the limits of St Paul's itself: as if he were playing the building as well as the orchestra. The detail of Bruckner's orchestration was lost in the scherzo third movement, but by the end of the finale, the physical features of the building, its acoustic, and the music had become a single entity.

Bruckner's symphonies are often described as cathedrals in sound; in this performance, the music was an expression and a transcendence of St Paul's' architecture.